Commercial dehumidification: when a building needs it and what it costs
Updated 23 October 2026 · SEO Dons Editorial
When does a commercial building need dehumidification?
A building needs it when moisture arrives faster than the building can lose it and the cause cannot be removed. Dantherm, a dehumidifier maker, says most problems with excess water in the air are caused by air change problems, and recommends finding the root cause because there are often ways to reduce or eliminate the problem before mechanical dehumidification is applied. Check leakage, open doors and uncontrolled ventilation first.
Where the load stays, the CIBSE Journal CPD module of February 2026 and other sources name the usual cases:
- Pool halls. CIBSE says sustained internal moisture generation makes them especially vulnerable, and that they typically need dedicated dehumidification to protect the building fabric. The pool humidity guide covers the design conditions.
- Museums, galleries and archives, where CIBSE says humidity stability is often more important than the absolute level. HMRC's valuation manual gives 35% to 60% relative humidity for archives.
- Industrial processes, where CIBSE says excess moisture can disrupt manufacturing, degrade product quality and shorten equipment life.
- Stores and warehouses, where Dantherm says the aim is usually to make sure relative humidity never exceeds a set level. See the warehouse page for the cooling side.
- Construction and water-damage drying. Its seller describes the Dantherm WDH 500AH as a construction dryer for larger rooms and water damage.
Server and comms rooms have their own page, the server room air conditioning guide.
Which technologies are there?
CIBSE Journal covers two established types: condensing and desiccant. It says neither is a universal solution.
| Condensing | Desiccant | |
|---|---|---|
| How it works | Cools air below its dew point so vapour condenses, then reheats it | A slowly rotating wheel of hygroscopic material such as silica gel adsorbs vapour and is regenerated with heated air |
| Air temperature | Typically 15 to 36°C; performance falls as the coil nears freezing | Typically about -30 to 40°C |
| Humidity target | Best above about 45 to 50% RH; comfort and building designs commonly 45 to 55% | Low humidity and low dew points, below about 50% RH |
| Control band | Wider, often around ±10% RH | Tighter, of the order of ±2% RH |
| Energy per kg of water | Approximately 0.5 to 1.5 kWh | Approximately 1.0 to 3.0 kWh, dominated by the regeneration heater |
| Installation | Usually an electrical supply and condensate drainage | Usually fixed; the regeneration exhaust must be ducted |
| Typical uses | Pool halls, moderate-humidity commercial and industrial spaces, museum and archive stores | Freezer stores, ice rinks, pharmaceutical and electronics manufacturing |
CIBSE adds that the plant can be duct-mounted or a self-contained non-ducted unit, and that combining the two can optimise capital and operating costs.
How is a dehumidifier sized from the moisture load?
From the water that has to be removed, not from a label. Dantherm sums four sources: people, process, goods and ventilation. The ventilation term is air density (about 1.2 kg per cubic metre) times room volume times air changes per hour times the difference in water content between outside and inside air, using the worst month for the outside figure. Hot months are the worst case because hot air holds more water.
An illustration, not a survey: take a 2,000 cubic metre store with 0.5 air changes an hour, where Dantherm gives 0.5 as its general fresh-air recommendation. Assume outside air at 12 g of water per kg of dry air and a target of 8 g/kg. Then 1.2 × 2,000 × 0.5 × 4 = 4,800 g an hour, or 4.8 kg an hour, before any people, process or stock are added.
Rating labels need the same care. Dantherm lists the DH 310 at 500 litres in 24 hours at 30°C and 80% RH, with an operating range of 1.5 to 42°C and a power input of 6.9 kW. Its smaller WDH 500AH shows how the output falls away at conditions nearer a real store:
| Room conditions | At 80% RH | At 60% RH |
|---|---|---|
| 30°C | about 50 litres a day | about 25 litres a day |
| 20°C | about 25 litres a day | about 14 litres a day |
| 15°C | about 18 litres a day | about 10 litres a day |
| 10°C | about 10 litres a day | about 7 litres a day |
CIBSE says robust moisture load calculations, supported by psychrometric analysis, are essential to avoid over- or under-sizing, and that latent loads are frequently dominated by ventilation air, infiltration or internal moisture generation. Selection should use the maker's output at the design inlet condition.
What does it cost to run?
No official source publishes unit prices, so none are given. Running cost can be built from CIBSE's energy ratios and an official tariff. DESNZ's 2025 provisional average for non-domestic electricity, all size bands and including the Climate Change Levy, is 24.3p per kWh, with gas at 5.3p per kWh. A given site's tariff will differ.
| Basis | Energy | Cost per kg of water removed |
|---|---|---|
| Condensing, all electric | 0.5 to 1.5 kWh | about 12p to 36p |
| Desiccant, if all the energy were electricity | 1.0 to 3.0 kWh | about 24p to 73p |
| Desiccant, if all the energy were gas heat, before boiler losses | 1.0 to 3.0 kWh | about 5p to 16p |
The desiccant rows are bounds: CIBSE does not split the total between heat and electricity, so the true figure depends on how the regeneration heat is supplied. Applied to the 4.8 kg an hour illustration, a condensing unit would use 2.4 to 7.2 kWh for each running hour, about 58p to 175p at 24.3p per kWh.
Arithmetic on makers' pages shows why the rating point matters. Dantherm's WDH 500AH lists 700 W at 20°C and 60% RH and about 14 litres a day there, roughly 1.2 kWh per litre, inside CIBSE's range. Reading the DH 310's 6.9 kW against its 30°C, 80% rating gives about 0.33 kWh per litre, but the page does not say which conditions the power figure refers to.
Where does a dehumidifying air handling unit fit?
CIBSE says dehumidification can reduce overall energy use by separating moisture control from temperature control. Where humidity is controlled only by cooling air below its dew point, systems may over-cool the air or need reheat. Lowering the building's dew point also lets radiant cooling such as chilled beams operate safely. The same module warns that moisture removal releases heat, which must be accounted for in the wider ventilation and cooling design.
That is the case for a dehumidifying section inside an air handling unit where a building already has ducted air, and for standalone units where it does not. The air handling unit guide explains the parts, and the steam versus adiabatic humidifier guide covers the opposite duty.
Control and care decide how it performs. CIBSE says simple humidistats may be enough for general commercial use, that dew point control is more accurate in precision applications, and that humidity sensors in unrepresentative positions can cause unstable operation or excessive energy use. Regular maintenance of filters, seals and drainage is essential. You can send an enquiry through the form on this site to ask for a moisture-load-based specification.
Sources
- Module 261: Condensing and desiccant dehumidifiers, CIBSE Journal, February 2026, checked 22 October 2026
- How to calculate the dehumidification load, Dantherm Group (manufacturer's own page), updated 28 November 2025, checked 22 October 2026
- Trotec DH 310 condensation dehumidifier, Dantherm Group (manufacturer's own page), checked 22 October 2026
- WDH 500AH dehumidifier, Dantherm Group AG (seller's product page), checked 22 October 2026
- DESNZ annual report and accounts 2025 to 2026: performance report, GOV.UK (DESNZ), updated 19 August 2026, checked 22 October 2026
- Rating manual: valuation of all property classes, archives, GOV.UK (HM Revenue and Customs), updated 21 September 2026, checked 22 October 2026
Common questions
Does a dehumidifier cool the space it serves?
No. CIBSE says dehumidification processes release heat: in desiccant systems adsorption is exothermic and the air typically leaves warmer, and in condensing systems latent heat is rejected at the condenser. Plan for that heat rather than counting on cooling.
Should the control signal be relative humidity or dew point?
CIBSE says simple humidistats may be enough for general commercial applications, while precision applications gain from dew point control, which is more accurate and less sensitive to temperature variation. Where air temperature swings, relative humidity alone can hide the true moisture condition.
What maintenance does a commercial dehumidifier need?
CIBSE says regular maintenance, including filter cleaning and inspection of seals and drainage, is essential to maintain performance. For a desiccant unit the regeneration exhaust must also be ducted, with attention to condensation risk and drainage.
Does an archive store need a desiccant unit?
Not automatically. HMRC's valuation manual gives 35% to 60% relative humidity for archives, and CIBSE lists museum and archive stores among the moderate-range uses of condensing units while saying desiccant suits targets below about 50% or tight control. The target and tolerance decide.
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